Rear Disc Brakes in an Early Bronco
Since so many requested the FAQ, here is a copy of what Toby sent me last year. It's very similar to what I wrote up years ago so this one should suffice. I will add two clarifications to what he wrote: the '79 Mark Vs came with 3/8" holes in the bearing retainer/caliper mount brackets. If you'd rather save the drilling step(to 1/2"), find the '76-'78 cars that already have 1/2" holes. I didn't do the machining step to bring the axle flange/bearing retainer clearance to the Lincoln spec; I check my brake pads often enough that letting them get to only 0.020" thick is not a reality for me. I also didn't use the stock Lincoln rubber lines. I've found that using a combination of pre-made hard lines and Earl's braided lines works well for me.
FWIW, Todd Z.
I have just finished the conversion to rear disc brakes with parking brake on my 77' HD axle housing using the parts off a 79' Lincon Mark V and hope this FQA will help others.
This will only work on the standard large bearing rearend. The years of Lincon Mark V to look for is 76' - 79'.
From the Junk yard I pulled the:
When I got home I pressed the bearing off the Mark V axles so I could remove the caliper mounting brackets. Once the brackets are removed the axles, bearings, and seals can be set aside in the corner of the garage to collect dust. At this time press the bearing, seal, and axle retaining plate off the 77' axle.
At this point I sized everything up and found that the four holes on the caliper mounting bracket/ bearing/seal retainer were of the small 5/1 diamater ( I think the 76' - 78' use the 1/2" studs ). The hole in the center of the rotor ( the brake register ) was larger than the hole in the drums where the end of the axle sticks through. The bolt pattern was differn't. The 77' axle flange was to large to fit inside the rotor.
So off to the machine shop I go. First enlarge the four holes and increase the nut face surface on the outboard side of the caliper mounting bracket/ bearing/seal retainer to accept the larger 1/2" studs. Then redrill the rotors to the 5 on 5 1/2 Bronco bolt pattern. Finaly turn down the O.D. of the 77' axle flange. I felt that the tolerances between the axle flange O.D. and the rotor I.D. were tight enough that I did not need to worry about how the hole in the center of the rotor was larger then the brake register on the end of the axle. Also have the flange to bearing offset on the 77' axle brought to the factory specs of the Mark V, by taking .250" off the end of the axle and the same off the bearing stop. The stock 77' offset is 2 3/8".
The stock Mark V offset is 2 1/8" ( I have herd that this step is not nessary if you use pre 76' - 78' Mark V brakes, but you will have to change the brake pads before the inner pad gets down to .020 or it will slip out of the caliper mounting bracket/ bearing/seal retainer ). The result is that the rotor and caliper are 1/4" further outboard on the caliper mounting bracket/ bearing/seal retainer than on the stock Mark V. This will let the inner brake pad fall out of the caliper mounting bracket/ bearing/seal retainer. Cost at machine shop = $120
You should also change your wheel studs to 3" long studs.
Place the caliper mounting bracket/ bearing/seal retainer on the 77' axle, then the seal ( a 3195 ), and bearing ( a A-20 ), then press the bearing retainer back on. If you want to run the rear shock in the stock position you need to mount the driver side ( on the Mark V ) caliper mounting bracket/ bearing/seal retainer on the passenger side axle, and vice versa. If youu plan on relocating the lower rear shock mount install the caliper mounting bracket/ bearing/seal retainer on the same sides as you took them off the Mark V. You can purchase the seal, bearing, and retainer as a set from Timken or Fedral Mougle as a part number of SET-20. Only use bearings made in the USA by Timken.
Install the axle and put the caliper mounting bracket/ bearing/seal retainer so the caliper mountes in the front of the axle ( opposite of the way it was mounted on the Mark V ). If you are running the stock lower shock mount. If you plan on relocating the lower shock mount, position the caliper mounting bracket/ bearing/seal retainer in the stock Mark V configuration. Install the four 1/2" studs through the axle flange and caliper mounting bracket/ bearing/seal retainer and tighten the nuts down.
Place the rotor on the axle, Install the caliper onto the caliper mounting bracket/ bearing/seal retainer.
Install flex line onto the caliper and the flex line mounting bracket. Find a good place on the axle tube to weld the bracket to and leave some slack in the flex line to be able to remove the caliper with out braeking the line ( caution: make sure to think about the U-bolt location and parking brake cables ). Cut the steel break line to the correct length and install the nut and redo the double flare.
Then make a small mounting bracket for the parking brake cable. I used the old shock mounts, reamed to the proper I.D. to accept the end of the cable and welded it to the bottom of the axle housing in the same position of the stock Mark V axle. Before welding make sure that the cable can work freely and does not bind.
I used a set of Wild Horses extended P-brake cables and a summit adj. proportioning valve on the rear line.
I hope this will help you bypass all the snags I ran into when I did my Bronco.
Toby Till 69' & 72' Bronco's EBR GBR OSA
Notes Courtesy of Sam Chambers, EBR #0202
I'd like to share my rear disk break experience. I use '78 Lincon Mark V calipers, caliper supports, rotors - the works. First it requires a big gearing rear end. The shafts must be turned down slightly and bearings removed. The caliper bracket slips on the shaft and a new bearing is then pressed on. The roters must be redrilled for a 5 on 5 1/2" bolt circle and the inside diameter turned larger (access to a lathe is helpful). Once this is completed, it is a bolt on setup.
Some spacing might be required to move the caliper toward the outside of the vehicle, 1/2" at maximum. A bearing retaining plate works well. The shock mounts will also have to be relocated inboard to clear the caliper. My costs are: $200 for calipers, caliper brackets, roters. $30 to redrill and turn rotors. New wheel bearings and relocating the shocks still left the total under $350, and they work great! I also use the master cylinder out of the Lincon with no proportioning valve or booster with no problems.